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/*! @m_page{{c,java},shared_cache,Per-process shared caches}
WiredTiger supports sharing a single cache among multiple databases within
a process.
An application configures a shared cache by specifying a shared_cache name
to the ::wiredtiger_open function. Applications can optionally
set a minimum amount of cache any connection in the pool will be assigned
and the granularity at which the cache pool is redistributed among
connections - called the chunk size.
The shared cache implementation assigns a certain amount of cache to each
participating database. Each database manages its allocated cache
as it would when not using a shared cache - thus databases using a shared
cache can have different eviction policies. There is a thread that monitors
the cache usage of each database and redistributes the cache among
participants according to where it is most likely to improve performance.
The cache is redistributed in chunks which are of a configurable size. Once
a database has had a chunk of cache added or removed it will be given
time to start effectively using that cache before it is considered for further
adjustment. If a small chunk size is configured it will take longer for the
shared cache to adjust to changes in participants. Reallocation of resources
happens periodically and whenever a database joins the shared cache.
The reallocation of resources is determined by comparing the amount of eviction
activity in a particular database to that of the other participating databases.
When a database is opened it will be allocated the amount of cache configured
as the shared cache minimum, regardless of whether the cache pool is currently
fully utilized. Other databases will have their assigned cache size
reduced so the total cache size used will return within the bounds - there
may be a period when the actual usage exceeds the configured maximum.
This is especially likely if many databases join the shared cache in a short
period. When a database is closed any resources it is using are distributed
among the other databases.
WiredTiger shared cache tuning options can be configured when first opening a
database via ::wiredtiger_open or changed after open using the
WT_CONNECTION::reconfigure method.
*/
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